Procedure and apparatus for drafting at least one fiber band

ABSTRACT

Proposed is a procedure and an apparatus for the drafting of at least one fiber band by means of a controlled preparatory drafting operation for a spinning machine, in particular a carding or a drafting frame, which possesses successively arranged roll-pairs ( 5, 6, 7 ) for corrective drafting, whereby the cross-section or the bulk, or the thickness of the at least one fiber band, or drafting from standard measurements is measured upstream of a roll-pair ( 5, 6, 7 ) and, based upon the corresponding measurement signals, the speed of rotation of at least one roll ( 5   a ) of a first roll-pair ( 5 ) is controlled by a first control circuit ( 30 ) and the rotational speed of at least one roll ( 6   a ) of a second roll-pair ( 6 ) is controlled by a second control circuit ( 35; 40 ). The procedure characterizes itself in that at least some of the measurement signals are so apportioned in partial amplitudes, that it is possible to form the total amplitude of the respective signal, and that band variations in a partial amplitude in the first control system ( 30 ) and variations in another partial amplitude in the second control system ( 35; 40 ) can be compensated. Likewise a corresponding apparatus is proposed.

The invention concerns a procedure for the drafting of at least one fiber band by means of a controlled spinning preparation machine, in particular a carding or drafting machine, which possess successively arranged correction roll-pairs, wherein the cross section, the bulk, or the thickness of the at least one fiber band or a variation thereof is measured upstream of the said roll-pair and on the basis of corresponding measurement signals, the rotational speed of an at least one roll of a first roll-pair is controlled by a first control circuit and the rotational speed of at least one roll of a second roll-pair is controlled by a second control circuit. Further, the invention concerns a corresponding apparatus in accord with the principal concept of claim 13.

Spinning-preparation machines such as carding or drafting machines serve the purpose of forming the greatest possible uniformity of textile material from the presented textile materials, notably, cotton, polyester, or mixtures thereof. To this end, the machines often possess a controlled drafting machine, in order to minimize existing band variations which are detected ahead of the drafting machine, such as variations in the cross-section, bulk or thickness. This minimizing of the said variations is effected by compensation organs successively situated in the running direction of the band. Upon drafting, these compensation organs consist, generally, of a plurality of roll-pairs, situated one after the other, between which the fiber band, or bands are pressed along a so-called clamping line in a transverse direction of the band. Since the roll-pair exhibits different, increasing circumferential speeds in the running direction of the band, the banding bonding of the said band or bands is drafted and made uniform. For the formation of data feedback in a closed control circuit or for the monitoring of variance compensation and possibly for prevention of a machine stillstand due to too great a variation of measured values of bands, to this is added, in most cases, a second measurement apparatus at the exit of the drafting frame.

To a great extent, mechanical direct contact apparatuses have been installed for the determination of the band cross-sectional measurements. For instance, the Rieter Draw Frame RSB D35 has a pair of direct contact disks with parallel axes, wherein the first disk is stationary and the second disk has the capability of moving in place, whereby a tension is formed against the first disk. The fiber bands are conducted through an opening between a circumferential groove of the first contact disk and a circumferential ring of the second contact disk, whereby the movable contact disk pivots in accord with the volume variations of the fiber band or fiber bands. These pivoting movements are transposed by a signal transducer into electrical voltage values, and transmitted for control of the roll-pair of the draft works to a data processor. The direct control is done at a the so-called “point of control”, which point defines that increment of the travel distance between the measuring device and the fictional drafting point in the drafting machine. Frequently, the said point of control finds itself at the same location as the said drafting point.

The point of control permits transmissions, which are of an educated empirical nature or are exactly in conformity with detected numerical values. This feature will not be further discussed here.

For the determination of band variations, an appropriate measuring device can detect the bulk, or the thickness and/or the cross-section of the fiber band. With mechanical band contact measurement, normally the cross-section of the band is determined at regular apportioned distances, for instance, every half centimeter. When microwave sensors are employed on the other hand, then the thickness is measured, in units of volume per unit of length.

Disadvantageous in the case of known drafting-correction apparatuses of preparatory machines of a spinning works, is, that the drafting-control of band variations, because of the inertial characteristics of the thereto assigned machine elements is not optimal.

Thus, it is the purpose of the invention, to so further develop the procedure, as well as the apparatus, of the type stated in the introductory passages, so that a precise variance compensation can be obtained of one or more fiber bands.

This purpose is achieved by means of the procedure and the apparatus, as mentioned in the said introductory lines and defined, respectively, by the features of the independent claims 1 and 13.

The values of the measurements as to bulk or as to the thickness, or yet to the cross-section of the at least one fiber band can be either absolute or related to a given constant value, whereby in the latter case, the band variations exhibit themselves as thickenings or thick locations of different lengths, or as sections of thin fiber band, again of different lengths.

The advantages of the inventions are especially to be observed in that the amplitudes of signals from the contact device, which device is located at the start of the drafting machine, must be processed in at least two control circuits, in order, that the freedom and precision of the control of the drafting correction apparatus, that is to say, the rolls, is increased. In this way, one partial amplitude of band variations sent to one control circuit can be subjected to drafting-control, while another partial amplitude of the band variation is corrected in another control circuit. The total regulation process is not furnished by a single roll-pair.

Accordingly, the invented apparatus characterizes itself, in accord with a preferred embodiment, in that, to each control circuit is assigned one thereto associated delay unit, namely a FIFO-memory, into which the voltage values which correspond to measurement signals can be temporarily held until a demand for disturbance control of partial amplitude is called for at a respective control-point. The two control-points are provided, in this matter, in different fields (i.e. drafting lengths) of the fiber band in the drafting machine which depart from the preselected dimensioning. These so-called fields are hereinafter designated as “drafting fields”.

In an advantageous and especially simple variant of an action, a firm ratio can be established, or is established, in regard to the apportionment of the partial amplitudes. If, for example, if 30% of band variations are allotted for correction in one control circuit, then in another control circuit, the remaining 70% is to be found, as determined by drafting-control. In case a third control circuit plays a role, then the apportionment is so regulated, that the sum of the partial amplitudes is likewise 100%. The ratio partitioning can, advantageously, be adjusted on the machine, and/or automatically adjusted, as long as preselected parameters have been input. The said parameters, for instance, would include the kind of material and/or known characteristics of the existing fiber. Also, it is possible, that the parameters may, in a particularly advantageous manner, include consideration of the machine dynamics or inertial moments.

Alternatively, a dynamic apportionment of the partial amplitudes can be undertaken, which can take cognizance of various criteria, namely, the size and occurring frequency of band variations. Also it is possible that a computer simulation on the basis of measurement signals received upstream of a drafting frame can be carried out, in order to more exactly compute the currently optimal amplitude apportionment.

The possibility exists, that greater partial amplitudes may present themselves, which are attributable to a driving string, wherein the respective rolls take their own part, are regulated to provide drafting-control. An advantage would lie in the said driving string possessing a relatively small inertia moment. Even so, smaller partial amplitudes can still be drafting-controlled, in a drive string with a greater inertia.

The apportionment of amplitude is advantageously undertaken before the voltage values of the measurement signals are sent to the temporary storage. In this respect, a measuring device with a lagging amplitude distributing circuit can be provided, wherein, on a static or dynamic basis, the entire amplitude, is divided into partial amplitudes, but biased on band variations and sends these biased partial amplitudes to selected delay units. Advantageously, the amplitude apportioning takes consideration of the fact, that the said control-points are different for each portion, so that the voltage values of the partial amplitude for the downstream control point are stored later in the corresponding delay unit, than are those for the upstream control-point.

Alternatively to the said amplitude distributor being set forward of the delay unit in the circuit, it is also possible that the amplitude apportionment, as well as the band travel and time offsets in regard to different control-point locations in the various drafting fields can even be calculated in a post-connected computer. For such an arrangement, various types of construction are possible. In the case of one embodiment, principally, a delay unit is provided between the measuring device and the computer, which in a known manner, temporarily stores the voltage value for the entire amplitude in accord with the FIFO method. The computer processes these values, then, in a double action. First, for the computation of the specified values for the first control circuit, in order to have these available for call-up on this control circuit, and then, second, to send said values for temporary storage in a second delay unit only after the computation of the thereto-attributable specified-partial amplitudes for the second control-circuit and for a subsequent call up, if the band piece to be drafted reaches a control-point in the drafting control part of the second control circuit.

The delay units, in which the voltage values to the various partial amplitudes are stored, in another embodiment, can be independent of one another. As an alternative, it is possible that the values in one delay unit can be related to the values in the other delay unit. In such a case, then the separating distance of the two thereto assigned control-points must be given consideration. For example, the voltage values in the one delay unit are multiplied with a factor, so that the sum of the voltage value in the two delay units yields the total amplitude of the band variations.

The procedure in accord with the invention, as well as the invented associated apparatus, are particularly advantageous, if, upon three successively following roll-pairs, an entry roll-pair and a middle roll-pair form an upstream (forward) drafting field, and the middle roll-pair together with the exit roll-pair create a downstream, subsequent main drafting field, and if, also, both the upstream as well as the downstream drafting, by means of control of the drive, can be changed by at least two of the three said roll-pairs.

The above mentioned embodiment of the invention also offers the advantage, that in the first control circuit, the rotary speed of at least one entry roll is controlled, and in the second control circuit, the rotary speed of at least one middle roll is controlled. By means of the speed of rotation of the entering roll-pair, in this case, a corrective drafting is acquired in the forward drafting field, as long as the rotary speed of the middle roll-pair exceeds the speed of rotation of the entry roll-pair. At the same time the control of the drive for the middle roll-pair, can exhibit an effect on both the forward corrective drafting as well as on the subsequent main corrective drafting. In one embodiment, the middle roll-pair is driven in such a manner, that it principally effects the main correction drafting. In this case, the entry roll-pair must be controlled at the same speed of rotation as the middle roll-pair, in order that at the moment of the drafting-control of band variations in the subsequent main drafting field, no further drafting is caused in the forward drafting field. During the main corrective drafting, it is necessary, in this particular embodiment, that the speed of the entry roll-pair must equal the speed of the middle roll-pair.

In a general sense, the meaning here is, that the upstream roll-pair of two successive roll-pairs, which are attached to different control circuits, generates a movement component which is equal to and synchronized with a downstream roll-pair, and which further, combines with the movement component of the drafting-control of a corresponding partial amplitude field, to make a total movement. The upstream roll-pair is also controlled on the basis of several superimposed rotational speed curves, which first, arise from the synchronization of the two successive roll-pairs, and second from necessary speed of rotation changes for the corrective drafting of the band section in the upstream drafting field.

The already mentioned drafting-control of band variations by means of entry and middle roll-pairs sets a condition, that both in the forward drafting field as well as in the main drafting field, a respective control-point exists, which marks a fictional but ideal drafting point for at least one fiber band in the respective drafting field. In accord with this, in the case of another embodiment, it is of advantage, if in each drafting field, at least one pressure rod is provided, which is placed, in or near to the current control-point. In this matter, the separating distance for the two pressure rods corresponds to the difference of the two control-points. However, it is not absolutely necessary, to provide at least one pressure rod in each drafting field.

If entry and middle roller pairs are regulated for control, then the exit roller pair—during the normal production operation, that is, not during start-up and shutdown of the machine—is either driven with a constant circumferential speed, or, likewise—in a third control circuit—is driven under control.

In an alternative embodiment, only the entry and the exit roller pairs are driven by control circuits which are separated from one another, while the middle roll-pair, in normal production operation runs at a constant speed.

In the immediately above case, the first control circuit is responsible for the entry roll-pair and the second control circuit regulates the exit roll-pair. It can also be possible that the controlled drive of the middle roll-pair is by means of a first control circuit and the controlled drive of the exit roll-pair is by means of a second control circuit, while the entry roll-pair is driven at a constant speed.

Considering all embodiments, it is advantageous, if, for the roller pairs, in each case, a separate drive is provided, preferably respectively an electric motor, which, at best, should be a servo-motor. The respective motors in this case can drive additional machine elements, advantageously by belt drives or the like. For example, it is possible for the electric motor for the entry roll-pair to run, simultaneously, a measurement roll-pair placed ahead of the drafting frame. Also, the electric motor for the exit roll-pair can drive a calender roll-pair placed following the drafting frame and if necessary, also a rotating disk for the storage of the drafted fiber band in a spinning can.

Additionally, for the invented, amplitude-centered drafting-control, more exactly, for the control in accord with partial amplitudes in various control circuits, it is advantageously possible that also other parameters, such as the magnitude of measured values involved can be taken into account, or for instance, consideration can be given to the relationship of measurement signal portions to various frequency ranges. Thus, it is possible to increase the total amplitude of a portion in a given control circuit, this being, for instance, dynamic apportionment, especially when a high-frequency band disturbance exists. If, for instance, a short, thick section is to be controlled, then a drive train with a relatively small inertial value can correct additional amplitude portions by driving the rolls in question quickly up to a necessary circumferential speed, and as well as quickly braking the same. In other words, it is possible, to use low frequency measurement signal portions for the control of machine elements (including rolls) with a greater inertial moment and to employ high frequency measurement signal portions for the control of machine elements (including rolls) with lower inertial moments.

At least one measuring device present at a drafting frame, for example, can be designed as a mechanical contacting apparatus, or as a condenser device, or yet as a microwave based sampling apparatus for at least one fiber band.

Advantageous developments of the invention are characterized by the features of the subordinate claims. In the following, the invention is described and explained in greater detail with the aid of the figures.

There is shown in:

FIG. 1 a schematic circuit arrangement in accord with a first embodiment of the invention,

FIG. 2 a schematic presentation of the drafting-control of thick and thin sections in the forward and in the main drafting fields,

FIG. 3 a schematic circuit arrangement in accord with a second embodiment, and

FIG. 4 a schematic circuit arrangement in accord with a third embodiment.

In FIG. 1 is shown a controlled drafting frame I for the drafting of at least one fiber band FB in accord with the invention. The drafting frame 1 possesses a forward drafting field, which can be defined as running from an entry roll-pair 5 to a middle roll-pair 6, as well as a main drafting field, wherein the latter runs from the said middle roll-pair 6 to an exit roll-pair 7. In the forward drafting field, in this embodiment, is a located a pressure rod 8 and in the said main drafting field, is to be found a pressure rod 9. In accord with embodiment per FIG. 1, band variations are subjected to drafting-control, first in the forward drafting and second in the main drafting fields. Accordingly, in each forward drafting field, in accord with the invention, a portion of the total amplitude relative to the band variations, as mentioned, is subjected to drafting-control.

A compacting funnel 2 and a measuring device 3 are installed at the entrance to the drafting frame. The measuring device 3 includes two upstream positioned sensing disks, wherein each of the said disks rotates in a direction counter to the other. The first sensing disk is fixed in its location, and the second is secured by a radial, pivotal linkage, which holds the said second disk in tension against the first. Additionally, in the measuring device 3, is integrated a signal transducer, which transposes the pivotal movements between the sensing disks into electrical potential values. Alternative to this arrangement, it is possible that other mechanical or immobile measuring devices can be installed, these, possibly operating on the principle of a capacitive metering capacity or with the aid of microwaves.

At the band exit of the drafting frame 1, a turn-around roll 10 diverts the now corrected fiber band FB′″ to enter a calender roll-pair 12, before which a non-woven material collection funnel is inserted. The calender roll-pair delivers the fiber band FB into a band conduit of a rotating disk 13, in order that the said fiber band FB may be stored in a spin-can 14 on a rotating platform 15. Integrated in the calender roll-pair 12 is a second measuring device (not further described), which feeds back to a computer unit 20 the cross-section or the bulk, or the thickness of the fiber band FB′″ at this point and additionally provides a monitoring of the same. For instance, the machine can be automatically shutdown upon an overstepping or understepping of given threshold values.

The voltage values provided by the forward located measuring device 3 are transmitted to a amplitude distributor 21, which is electrically bound to a repetitive impulse timer 4. The said impulse timer 4, which is coupled to one of the two sensing disks of the measuring device 3 (in FIG. 1, the upper disk) produces a given number of impulses per rotation of this said one sensing disk, whereby this number creates a measurement value for the so-called transport length of the at least one fiber band FB which is running through the measuring device 3.

In the amplitude distributor 21 the measured values (absolute values or relative values in regard to a constant band thickness or band cross sectional dimensioning, or a band bulk) which, when united, form a total amplitude, made discrete in accord with the impulse count of the interval timer 4 and apportioned into partial amplitudes. The division into partial amplitudes, in this arrangement, can be done, in accord with a preselected given ratio basis or can be dynamic, for example, with the simultaneous consideration of the frequency apportionment of the band draftings and/or the inertias of the respective drive strings of the various control circuits. In the case of consideration of dividing the frequencies, then, in the amplitude distributor, means for computation and evaluation must be available.

Voltage values are now transmitted from the amplitude distributor 21 to each of two delay units 16, 17, which, respectively, are formed from an electronic memory as a First-In-First-Out (hereinafter FIFO) storage, which is part of the computer unit 20. The computer unit 20 also includes, for example, a microcomputer with a microprocessor. Also, it is possible, that the amplitude distributor can be integrated into the said computer unit 20. In accord with the count of the interval timer, the voltage values in the delay units 16, 17 are time retarded, whereby accordingly, the path passed by the fiber band between the measuring device 3 and the respective fictional, that is, imaginary, drafting point in the forward drafting field or in the main drafting field becomes a computational parameter. The separating distance between the location of the measurement of the measuring device 3 and the respective point of drafting is also known as a control-point, hence, the drafting point in the respective drafting field will be designated as a “control-point”. As exactly as possible, at this said control-point, also the respective pressure-rod 8, 9 is placed. If the fiber band FB′ or FB″ with the same section to be corrected reaches the fictional drafting point in the forward drafting field, or, in the main drafting field of the drafting frame 1, then that value, which is stored in the delay units 16 or 17, is released to a data processor of the computer unit 20, in order, that in accord with the desired corrective drafting adjustment, the speed of rotation of the respective drafting frame rolls can be computed.

The amplitude distributor 21, in this case, is so designed, that it recognizes the control-points of the two said drafting fields. The reason for this recognition, is that the said control points have been empirically determined by the service personnel, or have been automatically calculated, and subsequently input for the subsequent said recognition. On this account, the voltage values with the partial amplitudes are transmitted, with time offset, to the delay units 16, 17. In this way, the data processor 19 receives voltage values at the same time from the delay units 16, 17, which values do not represent the band section location at those times, but rather the lagging voltage values, now advanced approximately to the control-points. The travel, that is to say, the equivalent time difference (whereby the latter, as well as the travel, is dependent upon the feed speed of the at least one fiber band FB) of the two control-points represents in FIG. 1 the separating distance of the two pressure rods 8, and 9. Alternatively, it is possible that the amplitude distributor 21 can transmit voltage values to the same band sections at the same time to the delay units 16, 17, whereby, subsequently, in the data processor the separating distance of the control-points is included in its computations.

For drafting-control in the forward drafting-field, a first control circuit 30 is provided, the controller 31 of which possesses a specified, set value for the cross-section, bulk and thickness of the fiber band FB′ exiting from the forward drafting field. This set value, or values, was imparted to the controller 31 from the data processor 19, in accord with the delayed voltage values of the delay unit 16. The controller 31 transmits this set value to the motor 32. The control in the control circuit 30 is completed by a tacho-generator 33, which backfeeds the speed of rotation of the motor 30 to the controller 31. The motor 31 additionally drives, besides the entry under-roll 5 a, also at least one sensing disk of the measuring device 3.

For the control of the middle roll-pair 6, the computer unit 20 transmits, in accord with the delayed voltage values of the delay unit 17, a set value to the second control circuit 35, and specifically to a controller 36 therein, which is connected to a tacho-generator 38, the motor 37 of which said circuit runs in a differential drive 24, which energizes the under-roll 6a of the middle roll-pair 6. The differential drive 24 receives from a main motor 22 a basic speed of rotation, which speed is adjustable by a rotational speed adjustment device 23 interposed between the main motor 22 and the said differential drive 24. The main motor 22, on its part, directly drives the under-roll 7 a of the exit roll-pair 7, whereby, from the said exit roll-pair, a constant band running speed is obtained. In addition, the motor 22 also drives at least one roll of the calender roll-pair 12.

FIG. 2 a schematically illustrates the curve of the amplitude ΔA of a band section to be subjected to drafting-control, which curves varies about a constant value for bulk, thickness or cross-section. After one thick position I, there follows a thin section I, onto which, in turn, a thick section II attaches itself. After the apportionment of this total signal, with a total amplitude in the amplitude distributor 21, then voltage values with partial amplitudes ΔA₁ and ΔA₂ (see FIG. 1), the sum of which is equal to the said total amplitude, are respectively saved in the delay units 16, 17. In the FIG. 2 b, these delay units 16, 17 are designated as FIFO 1 and FIFO 2. In the given presentation a statistical ratio of 1:2 has been selected. That is to say, 33% of the total drafting amplitude is to be found in the first control circuit 30 and 67% is to be controlled for drafting in the second control circuit. For the sake of simplicity, in FIG. 2 b the offset of the two control-points is not considered.

FIG. 2 c shows the compensation of the amplitude in the first control circuit 30 (above: drafting-control in the forward drafting-field) and in the second control circuit 35, (lower: the drafting-control takes place in the main drafting-field). The amplitude compensation in the first control circuit 30 is carried out by changes in the speed of rotation An of the lower entry roll 5a, whereby a functional connection exists to the partial amplitude which is to be subjected to drafting-control. For the compensation of the thick section I, the lower roll 5 a of the inlet pair must rotate slower (negative value of the solid line in FIG. 2 c, above), while for the correction of the thin section I, the entry under roll 5 a must accelerate) positive value for the dashed line in FIG. 2 c, above). In the case of the thick section II, it is necessary, that speed of rotation of the roll 5 a, conversely, must be further throttled (negative value of a dotted line in FIG. 2 c, above).

The thick section !, which is only partially compensated, subsequently reaches the main drafting-field, in which the remaining partial amplitude must be controlled for drafting by the second control circuit 35. Accordingly, it is now necessary that the middle under roll 6a must turn slower (negative value of the solid line in FIG. 2 c, below), while the exit under roll 7 a rotates at a constant circumferential speed. At the exit of the drafting frame 1, the thick section I has been thus corrected. A corresponding situation exists also for the thin section I as well as the thick section II in the main drafting-field. This latter is not shown.

In any case, consideration must be given, that a slower running of the middle under roll 6 a also causes reactions on the forward drafting-field. Since in this operation, no additional changing must occur because of the effect of corrective control in the main drafting-field, it is necessary that the entry under roll 5 a, must run at the same speed as the middle under roll 6 a upon the correction action for the thick section I. In other words, the entry under roll 5 a must be synchronized with the middle under roll 6 a (see negative value of the long-dashed, curve in FIG. 2 c, above). This synchronized component is to be summed up with the components for the drafting-control of the thick and thin sections in the forward drafting-field. Thus the summing gives rise to dashed line (as seen in FIG. 2 c, above, and marked “total” and for a better presentation, is given a small downward offset), which reflects the drafting control amplitudes, that is to say, the corresponding speed of rotation changes of the entry under roll 5 a.

In FIG. 1 is shown a graphic representation for this same-speed operation, that is, the said synchronization, symbolized by means of the dashed lines in the data processor 19. The drafting means, that the first control circuit requires the data from the second delay unit 17, in order to be able to take cognizance of the corresponding movement components. By means of a statistic apportioning, (see above) it is possible that these movement components can also be computed from the voltage values of the first delay unit 16 itself (always with the inclusion of the various control-points). Alternative to this, the speed of rotation of the middle under roll 6 a is measured, is fed back to the data processor 19 and there used for the necessary movement components of the entry under roll 5 a for obtaining the required value for synchronization.

In FIG. 3 is an alternative embodiment of the invented apparatus, wherein the separate drives for the entry roll-pair 5, the middle roll-pair 6 and the exit roll-pair 7 are provided. The drive string and the control circuit 30 for the entry under roll 5 a are identical to the embodiment example of FIG. 1. However, for the middle under roll 6 a is provided a thereto dedicated second control circuit 40 with a controller 41, a motor 42 and a tacho-generator 43. The corresponding drive string possesses only a very small inertial load and thus is advantageously able to take over a large portion of the total amplitude of the drafting control of the band variations from norms.

Also the exit under roll 7 a, is again driven through its own control circuit 50, with a controller 51, a motor 52 and a tacho-generator 53, wherein the motor 52 also drives a calender roll-pair 12. In the case of the embodiment as shown in FIG. 3, its own control circuit is nor required, if the drafting frame is to be operated at a constant production output, namely, a constant delivery rate. In such a situation, even an uncontrolled motor, corresponding to that of FIG. 1 would suffice (see FIG. 1, Motor 22).

In accord with the embodiment examples of the FIGS. 1 and 3, principally the entry roll-pair 5 and the middle roll-pair 6 were brought forward, whereby the apportionment of the total amplitude can be made to relate to the band variations by adjustments according to a set percentage or by a dynamic evaluation. In the case of the said dynamic evaluation, it can be possible, to evaluate the band variations additionally in accord with their frequencies, in order, for example, to control large corrections in a drive string with less inertial interference and less frequent error portions in a drive string with a greater inertial involvement.

In the embodiment example in accord with FIG. 3, the drive string for the middle roll-pair 6 possesses, for example, a relatively small inertial involvement, which the drive string for the exit roll-pair 7, on the other hand, shows a greater inertial load.

The embodiment in accord with FIG. 4, differentiates itself from that of FIG. 3, particularly in that a third control circuit 50 has been provided. By means of this additional control circuit 50, likewise a portion of the variation amplitudes can be corrected. The total amplitude is, on this account, divided in the amplitude distributor 21 into three partial amplitudes, on which account, three delay units are required. The repeated amplitude diagrams, i.e. based on speed-changes of rotation control, in FIG. 2 are, in this case very complex, but an be analogously presented. 

1. A procedure for the drafting of at least one fiber band (FB) by means of a controlled preparatory machine for a spinning works, in particular a carding machine or a drafting frame, which possesses successively aligned drafting control roll-pairs (5, 6, 7), whereby the cross-section, the bulk or the thickness of the at least one fiber band (FB) or the variation of one of these said measurement values upstream of the roll-pairs (5, 6, 7) is measured and based on the corresponding measurement signal the rotational speed of at least one roll (5 a) of a first roll-pair (5) is controlled by a first control circuit (30) and the rotational speed of at least one roll (6 a) of a second roll-pair (6) is controlled by a second control circuit (35: 40), therein characterized, in that at least some of the measurement signals are apportioned in such a manner into signals of partial amplitudes. which when summed, form the total amplitude of the current measurement signal, and in that a given part of band variations can be compensated in one apportioned part of the total amplitude in a first control circuit (30) and a remaining part can be compensated in a remaining apportioned part of the total amplitude in a second control circuit (35: 40). 2-33. (canceled) 